Search

A naphtho[2,1-b:6,5-b′]difuran derivative was found to serve as an effective violet-emitting laser dye. It showed amplified spontaneous emission at 413 nm with the threshold of 1.1–2.9 mJ cm−2 using 0.1–0.5 wt% in polystyrene film. Lasing was also demonstrated using all-polymeric distributed-feedback lasers emitting at 411–417 nm with the threshold of 2.0–2.9 mJ cm−2. This work was supported by JSPS KAKENHI grant JP19H05716 (to H. T.) and by the “Ministerio de Ciencia, Innovación y Universidades” of Spain, via grants MAT2015-66586-R and PID2020-119124RB-I00 and by the “Generalitat Valenciana” through grant AICO/2021/093.

The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (&lt, 5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light.

Chemically synthesized zigzag-edged nanographenes (NG) have recently demonstrated great success as the active laser units in solution-processed organic distributed feedback (DFB) lasers. Here, we report the first observation of dual amplified spontaneous emission (ASE) from a large-size NG derivative (with 12 benzenoid rings) dispersed in a polystyrene film. ASE is observed simultaneously at the 685 and 739 nm wavelengths, which correspond to different transitions of the photoluminescence spectrum. Ultrafast pump-probe spectroscopy has been used to ascertain the underlying photophysical processes taking place in the films. DFB lasers, based on these materials and top-layer nanostructured polymeric resonators (i.e., one or two-dimensional surface relief gratings), have been fabricated and characterized. Lasers emitting close to either one of the two possible ASE wavelengths, or simultaneously at both of them, have been prepared by proper selection of the resonator parameters. The Alicante team was funded by Spanish Government (MINECO) and European Community (FEDER), grant number MAT2015-66586-R. The researcher R.M-M was funded by a MINECO FPI fellowship (No. BES-2016-077681). The Singapore team was funded by the NRF Investigatorship programme (NRF-NRFI05-2019-0005). The Milan team has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 816313). G.M.P. acknowledges funding from Fondazione Cariplo, grant No. 2018-0979. C.D. and S.S. acknowledge funding from ERC Starting Grant SOLENALGAE (No. 679814).

10 pags., 7 figs., The increasing number of solution-processed laser compounds that can be implemented as low-cost, flexible, and/or integrated devices, makes necessary the development of reliable methods to delineate all their amplifying signatures and thus to open the door to appropriate cross-sample comparisons. Seeking to solve this problem, a new formalism to retrieve the losses and the optical gains from Amplified Spontaneous Emission (ASE) spectra as a function of the excitation density has been recently reported. In this manuscript, we explore the potential of this methodology to unveil relevant information on the photonic properties of the waveguiding devices and on the photophysics of the active materials. We demonstrate that the Variable Pump Intensity method opens the door to understand the relationship between the ASE thresholds and the optical gains and losses, it enables the extraction of the scattering/modal losses of the passive devices, and it can unveil the presence of leaky-modes and excited state absorption. In contrast, it does not perform too well in samples with multiple active species in its current implementation. We have substantiated all these findings using organic semiconductor thin films, several dye-doped polymer thin films and solutions of boron hydride., The researchers from the University of Alicante and LC acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and the European FEDER funds through Grant numbers MAT2015-66586-R and MAT2017-83856-C3-1, respectively.

Surface-emitting distributed feedback (DFB) lasers with both, resonator and active material based on solution-processable polymers, are attractive light sources for a variety of low-cost applications. Besides, the lasers should have competitive characteristics compared to devices based on high-quality inorganic resonators. Here, we report high performing all-solution-processed organic DFB lasers, consisting of water-processed photoresist layers with surface relief gratings located over the active films, whose emission properties can be finely tuned through resonator design. Their laser threshold and efficiency are simultaneously optimized by proper selection of residual resist thickness and grating depth, d. Lowest thresholds and largest efficiencies are obtained when there is no residual layer, while a trade-off between threshold and efficiency is found in relation to d, because both parameters decrease with decreasing d. This behaviour is successfully explained in terms of an overlap factor r, defined to quantify the interaction strength between the grating and the light emitted by the active film and traveling along it, via the evanescent field. It is found that optimal grating depths are in the range 100–130 nm (r ~ 0.5−0.4). Overall, this study provides comprehensive design rules towards an accurate control of the emission properties of the reported lasers.

The chemical synthesis of nanographene molecules constitutes the bottom-up approach toward graphene, simultaneously providing rational chemical design, structure-property control and exploitation of their semiconducting and luminescence properties. Here, we report nanographene-based lasers from three zigzag-edged polycyclic aromatics. The devices consist of a passive polymer film hosting the nanographenes and a top-layer polymeric distributed feedback resonator. Both the active material and the laser resonator are processed from solution, key for the purpose of obtaining low-cost devices with mechanical flexibility. The prepared lasers show narrow linewidth (, Chemically synthesized graphene nanosheets offer device design flexibility and improved optoelectronic performance. Here, the authors report solution-processed distributed feedback lasers with graphene nanosheets as active media having linewidths

Latest advances from our research group towards improving the performance of solution-processed distributed feedback lasers will be discussed. They include advances on the laser material and the resonator and their application as optical sensors.

Two-dimensional (2D) distributed feedback (DFB) lasers with gratings imprinted by thermal nanoimprint lithography on the active film are reported. They show thresholds for lasing of ∼10 kW/cm2, similar to the most efficient imprinted DFB lasers reported; and long operational lifetimes (under ambient conditions) of ∼12 × 104 pump pulses. The key for their successful operation has been the selection of a highly efficient and stable dye, perylene orange (PDI-O), and a proper matrix to host it, the fluoro-modified thermoplastic resist mr-I7030R, which has enabled 2D imprinting while preserving the dye optical properties. The use of the UV-curable resist SU8 as an alternative matrix for PDI-O to be imprinted by combined nanoimprint and photolithography was also investigated, and was concluded to be unsuccessful due to severe photoluminescence quenching. By replacing PDI-O with Rhodamine 6G, lasers with reasonable thresholds, but with significantly inferior operational lifetimes in comparison to PDI-O/mr-I7030R devices, were obtained., We thank support from the Spanish Government (MINECO) and the European Community (FEDER) through Grants MAT2011-28167-C02 and MAT2015-66586-R, as well as to the University of Alicante. M.M-V. has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747) and by a Junta de Castilla y León grant (no. SA046U16).

In the present work thermal-nanoimprint lithography of various commercial thermoplastic resists as matrixes for perylenediimides (PDIs) has been studied. This fabrication method reduces the number of fabrication steps, and therefore, the cost of the obtained distributed feedback (DFB) lasers. The optical properties of these devices are analyzed, aiming to optimize their performance. Spanish Government (MINECO) and the European Community (FEDER) through grants MAT2008-06648-C02 and MAT-2011-28167-C02. Manuel G. Ramírez is supported by a CSIC fellowship within the program JAE.

Thin film organic lasers represent attractive light sources for numerous applications. Currently, efforts are devoted to the development of low-cost high-performance and color-tunable devices, whereby both the resonator and the active layer should consist of solution-processable organic materials. Herein, solution-processed distributed-feedback lasers are reported with polymeric resonators on top of active films of perylene orange or carbon-bridged oligo(p-phenylenevinylene) dispersed in polystyrene, which combine these properties. These lasers emit in the 520–595 nm range and show low thresholds (≈1 kW cm−2) and long operational lifetimes (7 × 105 pump pulses), which are comparable to other state-of-the-art lasers that contain the same active materials but resonators made on inorganic substrates. Due to this top-layer resonator configuration, the laser slope efficiencies of the present devices are remarkably superior. A centimeter-size device emitting at different wavelengths within a broad spectral range, based on a perylene-based film of uniform thickness that contributes to preserve a low threshold, is demonstrate, MINECO. Grant Numbers: MAT2011-28167-C02-01, MAT2015-66586-R, BES-2009-020747 Junta de Castilla y León. Grant Number: SA046U16 MEXT. Grant Numbers: 16H04106, 15H05754

This paper aims to review the recent advances achieved in the field of organic solid-state lasers with respect to the usage of semiconducting organic molecules and oligomers in the form of thin films as active laser media. We mainly focus on the work performed in the last few years by our research group. The amplified spontaneous emission (ASE) properties, by optical pump, of various types of molecules doped into polystyrene films in waveguide configuration, are described. The various systems investigated include N,N´-bis(3-methylphenyl)-N,N´-diphenylbenzidine (TPD), several perilenediimide derivatives (PDIs), as well as two oligo-phenylenevinylene derivatives. The ASE characteristics, i.e., threshold, emission wavelength, linewidth, and photostability are compared with that of other molecular materials investigated in the literature.

Two critical temperatures, T1 and T2, which limit the range of the photorefractive (PR) response of polymer composites, have been determined from temperature dependence studies of the ac conductivity. T1 represents the calorimetric glass transition temperature and sets the level under which chromophore orientation is drastically reduced. T2 sets the level above which conduction mechanisms become dominated by temperature. In this study, we stress the importance of the T2 parameter, generally ignored in literature, and the advantages of using dielectric spectroscopy to obtain both critical temperatures from a single experiment. In addition, impurity diffusion processes, which play an important role in PR property optimization, have been identified from the frequency dependence of the ac conductivity.

Solution-processed polymer films are used in multiple technological applications. The presence of residual solvent in the film, as a consequence of the preparation method, affects the material properties, so films are typically subjected to post-deposition thermal annealing treatments aiming at its elimination. Monitoring the amount of solvent eliminated as a function of the annealing parameters is important to design a proper treatment to ensure complete solvent elimination, crucial to obtain reproducible and stable material properties and therefore, device performance. Here we demonstrate, for the first time to our knowledge, the use of an organic distributed feedback (DFB) laser to monitor with high precision the amount of solvent extracted from a spin-coated polymer film as a function of the thermal annealing time. The polymer film of interest, polystyrene in the present work, is doped with a small amount of a laser dye as to constitute the active layer of the laser device and deposited over a reusable DFB resonator. It is shown that solvent elimination translates into shifts in the DFB laser wavelength, as a consequence of changes in film thickness and refractive index. The proposed method is expected to be applicable to other types of annealing treatments, polymer-solvent combinations or film deposition methods, thus constituting a valuable tool to accurately control the quality and reproducibility of solution-processed polymer thin films. The work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant No. MAT-2011-28167-C02-01. M.M.-V. has been partly supported by a MINECO FPI fellowship (No. BES-2009-020747).

Thin film organic lasers represent a new generation of inexpensive, mechanically flexible devices for spectroscopy, optical communications and sensing. For this purpose, it is desired to develop highly efficient, stable, wavelength-tunable and solution-processable organic laser materials. Here we report that carbon-bridged oligo(p-phenylenevinylene)s serve as optimal materials combining all these properties simultaneously at the level required for applications by demonstrating amplified spontaneous emission and distributed feedback laser devices. A series of six compounds, with the repeating unit from 1 to 6, doped into polystyrene films undergo amplified spontaneous emission from 385 to 585 nm with remarkably low threshold and high net gain coefficients, as well as high photostability. The fabricated lasers show narrow linewidth (105 pump pulses for oligomers with three to six repeating units) and wavelength tunability across the visible spectrum (408–591 nm)., Thin film organic solid-state lasers are low-cost flexible devices which require efficient, stable, colour-tunable, solution-processable materials. Here, the authors show that oligo(p-phenylenevinylene)s simultaneously possess all such properties, as demonstrated by their use in laser devices.

Distributed feedback (DFB) laser sensors with active films consisting of a highly efficient and photostable perylenediimide dye (perylene orange, PDI-O) dispersed in polysytrene (PS), used as passive matrix, are reported. PDIdoped- PS DFB lasers show an excellent operational durability under ambient conditions, superior to those of previously reported DFBs used for sensing purposes. Their bulk refractive index sensing capabilities, under exposure to liquids of different refractive index, have been determined from changes in their emission wavelength. The role of the active film thickness on both, the laser and the sensing performance, has been explored. The use of a thick active film (850 nm) allows obtaining the lowest possible threshold and highest operational lifetime for this type of device although the sensor sensitivity is lower than that achievable with a thin film (160 nm). It is also shown that the inclusion of a high refractive index TiO2 layer on top of the sensor structure allows improving the sensor sensitivity by around two times. This work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant no. MAT-2011–28167-C02. M.M-V. has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747).

The refractive index sensing capabilitity of distributed feedback (DFB) lasers based on highly photostable (under ambient conditions) perylenediimide-based active films, are reported. The sensor bulk sensitivity is determined from changes in the laser emission wavelength upon exposure to different liquids. The role of the active film thickness (hf) on the sensor sensitivity and on the laser parameters is studied. Sensors based on very thin films (hf = 160 nm) show the highest sensitivities, but their laser thresholds are relatively high and their operational durabilities moderate. The use of thicker films (hf = 850 nm) allows reducing the laser threshold and increasing the durability by two orders of magnitude. In this case, a higher sensitivity is achieved when the sensor operates at the wavelength corresponding to the first-order TE1 mode, instead of at the TE0 one. Finally, it is also shown that the inclusion of a high refractive index TiO2 layer on top of the sensor structure improves the sensitivity by around two times. This work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant no. MAT-2011–28167-C02. This work was partially funded by the Basque Government within the framework of the Etortek Program (Grant No. IE13-360). M. Morales-Vidal has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747).

Laser action at 420 nm is observed in photopumped polymer films of polystyrene (PS) doped with the hole-transporting organic molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD). Measurements of the dependence of signal on the length of the pump stripe show that the mechanism responsible for the observed spectral collapse is amplified spontaneous emission (ASE). By fitting the evolution of the output intensity at 420 nm with the excitation length, gain coefficients up to 16 cm-1 are measured.

A series of novel trinitrofluorenone−C60 acceptors in which the two subunits are placed at different distances have been prepared and their electrochemical and photorefractive properties measured. The photorefractive performance of these compounds as sensitizers in polymer composites based on poly(N-vinylcarbazole) is similar to that of C60, but with shorter response times and slightly lower gain coefficients. Since the substitution of C60 by these novel trinitrofluorenone−C60 systems leads to a reduction of losses due to beam fanning, larger voltages could be applied, resulting in larger gain coefficients.

Thin film organic lasers (TFOLs) represent a new generation of inexpensive, mechanically flexible devices with demonstrated applicability in numerous applications in the fields of spectroscopy, optical communications and sensing requiring an organic, efficient, stable, wavelength-tunable and solution-processable laser material. A distributed feedback (DFB) laser is a particularly attractive TFOL because it shows single mode emission, low pump energy, easy integration with other devices, mechanical flexibility and potentially low production cost. Here, amplified spontaneous emission (ASE) and DFB laser applications of novel high performing perylene dyes and p-phenylenevinylene (PV) oligomers, both dispersed in thermoplastic polymers, used as passive matrixes, are reported. Second-order DFB lasers based on these materials show single mode emission, wavelength tunability across the visible spectrum, operational lifetimes of >105 pump pulses, larger than previously reported PV oligomers or polymers, and thresholds close to pumping requirements with light-emitting diodes. This work was supported by the Spanish Government (MINECO) and the European Community (FEDER) through grant no. MAT-2011–28167-C02. M. Morales-Vidal has been partly supported by a MINECO FPI fellowship (no. BES-2009-020747).

A highly photostable distributed feedback (DFB) laser has been fabricated by spin-coating a polystyrene film doped with a perylenediimide derivative on a SiO"2 grating. The second-order grating, with a period of 368nm, was fabricated via thermal nanoimprint lithography and pattern transfer. When the DFB laser is photopumped at 533nm, the laser emission spectrum shows two peaks at 573 and 581nm. The laser threshold (I"t"h) is 30 times lower than the amplified spontaneous emission threshold for a sample without grating. These devices are very photostable: the halflife is longer than 100,000 pump pulses at a pump intensity of [email protected]/pulse.

In this work we study the effect of different types of modifications of the chemical structure of perylenebisimide derivatives (PBIs) in the laser properties of PBI-doped polystyrene films at various concentrations. In particular, we focus on controlling the wavelength of emission, in order to tune the laser wavelength, as well as on increasing the amount of PBI in the films, aiming to decrease the laser thresholds, while keeping a good photostability. Amplified spontaneous emission (ASE) was observed for all compounds, the best performance being obtained for films doped with PBIs symmetrically substituted at the imide positions, that emitted at 580 nm with a threshold of 20 kW/cm 2 and a photostability half-life of 30,000 pump pulses. Substitution at the bay positions of the PBI core and replacement of imide functions by anhydride groups allow to red-shift the emission wavelength up to 645 nm, but the thresholds increase considerably and the photostability is reduced. PBIs are among the most photostable materials reported in the literature and show very reasonable thresholds. In addition they have a great potential for their application in the field of data communications based on poly(methyl methacrylate) optical fibers, with low-loss transmission windows between 530 and 590 nm and at 650 nm.

A new method for using dichromated gelatin films in photolithography has been recently developed in our laboratory. In this paper, we describe the experiments carried out for making efficient surface-relief diffraction gratings using that method. Basically, gratings are obtained by developing, in an oxygen electron cyclotron resonance stream, the interference of two coherent waves recorded on a dichromated gelatin film. Diffraction efficiency and incident angle selectivity of 0.5 μm period gratings are studied as a function of development time, and results are compared with theoretical predictions.

The aim of this work was to improve the laser performance, in terms of threshold and operational lifetime, of lasers based on polymer films doped with perylenediimide (PDI) derivatives as active media. For such purpose, we first investigated the amplified spontaneous emission (ASE) properties of perylene orange (PDI-O), when doped into polystyrene (PS) films. Lower ASE thresholds and larger photostabilities than those of similar films containing another PDI derivative (PDI-C6), recently reported in the literature, have been measured. Results have been interpreted in terms of the photoluminescence efficiency of the films, which depends on the type of molecular arrangement, inferred with the help of nuclear magnetic resonance experiments. We also show that PS films have a better ASE performance, i.e. lower thresholds and larger photostabilities, than those based on poly(methyl methacrylate), which was recently highlighted as one of the best matrixes for PDI-O. Finally, a one-dimensional second-order distributed feedback laser using PS doped with PDI-O was fabricated and characterized. This device has shown a threshold significantly lower (by around one order of magnitude) than that of a similar laser based on PDI-C6-doped PS. We thank support from the Spanish Government (MECC) and the European Community (FEDER) through grants MAT2008-06648-C02 and MAT-2011-28167-C02, as well as from the University of Alicante. MGR and MM are supported respectively by a CSIC fellowship within the program JAE and by MEC through a FPI fellowship.

Three-in-one: A novel distyrylbenzene-based material forms J-type aggregates in single crystals with highly polarized and bright red emission, giving rise to optical gain narrowing, for which different mechanisms (amplified spontaneous emission, laser emission and stimulated resonance Raman scattering) are observed. These are correlated with the favorable intrinsic and macroscopic properties of the crystal, in particular to the orientation of the molecules to the crystal surface.

The effect of varying film thickness (h) on the amplified spontaneous emission (ASE) properties of 0.5 wt.% perylenediimide-doped polystyrene waveguides is reported. The threshold dependence on h, not previously investigated in detail, is analyzed in terms of the film absorption and photoluminescence, the confinement of the fundamental waveguide mode (TE0), and the presence of high-order modes. For h < 400 nm and down to 150 nm, the ASE wavelength blueshifts, while the linewidth and threshold increase. The detrimental ASE operation in very thin films is due to the low absorption as well as to the poor confinement of the TE0 mode. Support from the Spanish Government (MEC) and the European Community (FEDER) through grants MAT2008-06648-C02 and MAT2011-28167-C02 and from the University of Alicante through grant GRE10-07. M. G. R. is supported by a CSIC fellowship within the program JAE.

We report on the fabrication of efficient organic distributed feedback (DFB) lasers with thermally-nanoimprinted active films, emitting between 565 and 580 nm. The use of thermal-NIL has allowed, as opposed to room temperature or solvent-assisted techniques, high grating quality and excellent modulation depth. The 155°C heat exposure of the NIL process, does not significantly affect the thermal and optical properties of the active material (polystyrene films doped with a perylenediimide derivative). These devices combine a simple and low-cost preparation method with good laser characteristics, i.e. thresholds of 1 μJ/pulse, single-mode emission with linewidths below 0.2 nm and photostability half-lives of ~ 105 pump pulses under ambient conditions. In comparison to more standard DFBs with gratings on the substrate, their fabrication is much easier, while they show a similar laser performance.

We present a method for increasing the bandwidth of reflection holograms in dichromated gelatin. The recording plate has two dichromated-gelatin layers of different hardness so that their shrinkage at the end of processing is different. We use this method for doubling the bandwidth of holographic mirrors that are designed for solar UV energy concentration. We also study the superposition of two double-layer holograms, which results in UV holographic mirrors with a bandwidth of 60 nm.

The spectral response of broadband reflection holograms in dichromated gelatin is studied; conditions for obtaining 100-nm bandwidth and 80% diffraction efficiency holograms are given. The structure of these holograms is discussed, and the scanning electron microscope is used to investigate fringe-spacing variations.

The fabrication and characterization of highly efficient and photostable second-order distributed feedback lasers (DFB), based on polystyrene films doped with a perylenediimide (PDI) derivative as active laser material, is reported. DFB gratings were obtained via thermal nanoimprint lithography and transferred to SiO 2 substrates by reactive ion etching. The influence of the PDI concentration on the laser performance has been investigated. The best results were obtained for the device based on the 0.5 wt% PDI-doped film, that emits at a wavelength of 571 nm, with a threshold of 2.5 μJ/pulse and a photostability halflife of around 500 min; i.e. 300000 pump pulses. The effectiveness of the DFB grating is evidenced by the decrease in threshold in two orders of magnitude with respect to the amplified spontaneous emission threshold obtained for a similar film deposited over a SiO 2 substrate without grating.

On montre que les caracteristiques de l'hologramme sont similaires a celles obtenues en partant des plaques Kodak 649F si le degre initial de durcissement de la gelatine est egal a celui des plaques 649F

Single-mode second-order distributed feedback (DFB) lasers with low threshold, based on polystyrene films doped with 30 wt:% of the hole-transporting organic molecule N,N0-bis (3-methylphenyl)-N,N0- diphenylbenzidine (TPD) are reported. The laser emission wavelength was tuned between 415 and 427nm by film thickness variation. The effectiveness of the DFB grating in improving the laser performance is evidenced by the observation of linewidths and laser thresholds lower than those of the amplified spontaneous emission characteristics shown by films without gratings. The use of holographic lithography as the technique for grating recording has allowed us to prepare large samples in a fast, versatile, and simple manner., The authors acknowledge support from the Spanish Ministerio de Educación y Ciencia (MEC), the European Community (FEDER)(grants MAT2005-07369-C03-01 and MAT2008-06648-C02-01) and the University of Alicante (grant VIGROB2005-060).We also thank V. Esteve for technical assistance.

The concentration dependence of amplified spontaneous emission (ASE) in optically pumped polystyrene (PS) films containing a variable concentration (between 2.5 and 100 % by weight (wt)) of the luminescent and hole-transporting organic molecule N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) is studied. It is observed that the photoluminiscence (PL) efficiency, the ASE threshold and the linewidth above threshold, decrease with concentration up to 20 wt % doped films and then keeps a constant value up to concentrations of 100 wt % (neat films). The position of ASE can be tuned between 413nm and 421 nm by changing the concentration of TPD. It was also possible to tune the ASE position (between 404 and 417 nm) trough control of the film thickness (between 100 and 200 nm). The observed shifts of the ASE position due to changes in concentration are determined by the PL efficiency (not by the waveguiding characteristics of the films). On the other hand, the observed shifts in the ASE position due to changes in film thickness depend on the shape of the PL spectrum and on cut-off thickness limitations. In this case, the ASE thresholds depend on the different confinement of the propagation modes due to thickness variations.

One dimensional second-order distributed feedback (DFB) lasers consisting of polystyrene (PS) films doped with a perylenediimide laser dye, deposited over dichromated gelatine (DCG) photoresist layers with solvent resistant relief gratings recorded by holographic lithography, are reported. The advantage of using the grating on DCG in the final device is that the fabrication process is simplified and the grating pattern better preserved, since no etching methods to transfer the grating to another substrate are needed. A very simple model, proposed to explain the experimental waveguide properties, has allowed identifying the waveguide mode at which DFB emission appears, which was the key to optimize the device performance. In the frame of this model, the thickness of the PS and DCG films could be adjusted in order to minimize the laser threshold and to control its wavelength tuneability. The performance of these lasers is comparable to that of recently reported devices based on the same active material, but deposited over high-quality DFB gratings engraved on SiO2 by nanoimprint lithography. We thank support from the Spanish Government (MINECO) and the European Community (FEDER) through Grant Nos. MAT2008-06648-C02 and MAT-2011-28167-C02, as well as to the University of Alicante. M.G.R. was supported by a CSIC fellowship within the program JAE.

We report on the preparation and characterization, under optical pump, of second-order one-dimensional distributed feedback (DFB) lasers based on polystyrene films doped with a perylenediimide derivative, as active media. The DFB gratings were engraved on the substrates (SiO2) by thermal nanoimprint lithography, followed by reactive ion etching. Laser emission wavelength was tuned from 554 to 583 nm by changing film thickness (h) between 240 and 1200 nm. The effect on the performance (emission wavelength, threshold, slope efficiency, number of modes, and spectral shape) of varying the grating depth (d) from 30 to 240 nm, for the whole range of h values, has been investigated. Although there is extensive work in the literature aiming to tune the emission wavelength of organic DFB lasers by h variation, the effect of changing d systematically has not been previously studied. Experimental results have been interpreted by models that take into account the presence of the grating by averaging either h or the e...

An efficient, low-cost, and highly photostable second-order distributed feedback (DFB) laser, fabricated by thermal nanoimprint lithography and based on a polymer active film containing a perylenediimide derivative, is reported. It shows a photostability half-life of 3.1×105 pump pulses (>8 h), when pumped at the same spot of the film. This value is the highest reported to date for organic DFB lasers measured under ambient conditions. The device emits at 573 nm, matching the second low-loss transmission window of poly(methylmethacrylate) (460–590 nm), thus offering potential for applications in data communications based on polymer optical fibers.

The presence of amplified spontaneous emission (ASE) by optical pump in polystyrene films doped with N,N'-di(10-nonadecyl)perylene-3,4:9,10-tetracarboxylic diimide (PDI-N) in a range of PDI-N concentrations between 0.25 and 5 wt. % is reported. Gain coefficients up to 10 cm(-1), at a pump intensity of 74 kW/cm2, were obtained. The lowest thresholds (approximately 15 kW/cm2) and largest photostabilities measured at 50% (approximately 50 min, i.e., 30,000 pump pulses) were obtained for concentrations up to 1 wt. %. The observation of an increase in the ASE threshold and a decrease in the photostability for larger concentrations is attributed to the presence of aggregated species.

We report on the photorefractive (PR) properties at the 633nm laser wavelength of a polymer composite based on the polymer poly(n-vinyl carbazole) (PVK), doped with the dicyanostyrene derivative 4-piperidinobenzylidene-malonitrile (PDCST) as nonlinear optical chromophore and the liquid plasticizer butyl benzyl phthalate (BBP), without the presence of sensitizer. The PR-effect is observed only when samples are previously subjected to an electric field (i.e., 20V∕μm for 10min). Photoconductivity and birefringence of the composite become significant when the electric field treatment is performed at temperatures higher than room temperature (24°C). Gain coefficient and PR speed, determined from two-beam coupling experiments, are compared to those obtained with the PVK∕PDSCT∕BBP∕C60 standard sensitized composite.

The thickness dependence of amplified spontaneous emission (ASE) in optically pumped polystyrene films containing 15 wt % of the luminescent and hole-transporting organic molecule N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) is reported. It is observed that the position of ASE can be tuned between 404 and 417 nm by changing the film thickness from 100 to 200 nm. By measuring and modeling the waveguide modes, we demonstrate that the calculated cut-off thickness for the propagation of one mode determine the thickness below which ASE disappears although they do not perfectly correlate with the observed wavelength shifts. Results show that the position of ASE depends on the shape of the photoluminescence spectrum, that is composed of various vibronic peaks whose relative intensities change with film thickness due to the existence of the cut-off thickness. Finally, it is also observed that both the position and the threshold of ASE depend on the different confinement of the propagation modes due to th...

We report on the design and the construction of a 1.3-m(2) UV selective solar concentrator intended for photocatalytic water detoxification processes. This concentrator was made by assembling 30 cm x 30 cm line-focusing holographic mirrors. Holograms with an 80% diffraction efficiency concentrate ~40% of the incident solar energy, which is effective for exciting an aqueous suspension of the TiO(2) photocatalyst, and transmit unnecessary longwave radiation. Major problems, such as the low sensitivity of the dichromated gelatin used for recording the holograms and wavelength dispersion, are discussed.

Solar holoconcentrators based on transmission holograms as well as reflection holograms have been designed. In the first case we have shown that silver-halide gelatin, which has a light sensitivity ≈103 times better than dichromated gelatin, is an alternative. In the second case we have developed methods to make broad-band violet spectrally responsive holoconcentrators.

A method for displaying ordinary transmission holograms with a white light source is described, based on compensating the color dispersion in a broad band of the visible spectrum. Although some degree of image blur remains because of the size of the source, sharp and bright images at 30 cm from the hologram plane have been reconstructed.